新疆祁漫塔格花土沟地区中酸性侵入岩的年代学、地球化学特征及其地质意义

Geochronology,Geochemistry and Geological Significance of the Huatugou Intermediate-acid Intrusions at Qimantag,Xinjiang

东昆仑祁漫塔格志留纪到泥盆纪岩浆活动强烈,其形成与大洋岩石圈俯冲造山、碰撞-后碰撞造山活动有关。本文对东昆仑祁漫塔格花土沟地区花岗闪长岩开展锆石U-Pb年代学、全岩地球化学研究,探讨岩石成岩过程及构造背景。花岗闪长岩LA-ICP-MS锆石U-Pb定年结果为(396.5±4.6)Ma,为早—中泥盆世岩浆活动产物。全岩SiO_(2)含量为63.01%~74.70%,显示高K_(2)O(1.53%~4.01%)、Na_(2)O(2.16%~3.80%)和Al_(2)O_(3)(12.95%~14.48%)特征,Mg#为17.01~61.23,属钙碱性-高钾钙碱性系列岩石。稀土元素球粒陨石标准化配分曲线呈中等倾斜的右倾平滑型曲线,具有负铕异常(δEu=0.48~0.72),微量元素蛛网图显示富集Rb、Th、La、Ce等大离子亲石元素和轻稀土元素,亏损Nb、Ta、Ba等高场强元素,属I型花岗岩。结合岩体成岩年龄、地球化学特征与区域构造演化,认为花岗闪长岩为造山带地壳物质特别是增生地壳物质的部分熔融,有幔源物质的混入,演化过程中经历了长石等矿物的结晶分离作用,形成于大陆碰撞造山末期向后碰撞转化阶段下的挤压向伸展过渡的构造环境。

The Qimantag in East Kunlun orogen has strong magmatic activity from the Silurian to Devonian,and its formation is related to oceanic lithosphere subduction orogeny and collision-post-collision orogeny.In this paper,zircon U-Pb chronology and whole-rock major and trace element geochemistry are carried out on the Hua-tugou granodiorite in Qimantag,and the petrogenesis and tectonic background are discussed.LA-ICP-MS zircon U-Pb dating of the granodiorite is(396.5±4.6)Ma,which is the product of Early-Middle Devonian magmatic activity.The whole-rock SiO_(2) content is 63.01%-74.70%,showing characteristics of high K_(2)O(1.53%-4.01%),Na_(2)O(2.16%-3.80%)and Al_(2)O_(3)(12.95%-14.48%),Mg#is 17.01-61.23,belonging to calc-alkaline and high-K calc-alkaline series.The chondrite-normalized REE patterns are moderately right-dipping and smooth,with negative Eu anomaly(δEu=0.48-0.72).Trace element spider diagram shows that the rocks are enriched in large ion lithophile elements(LILEs),such as Rb,Th,La,Ce and light rare earth elements(LREEs),and is depleted in Nb and Ta,Ba and other high field strength elements(HFSEs),belonging to I-type granite.Combined with the magmatic age,geochemical characteristics and regional tectonic evolution,we considered that the granodiorite is the partial melting product of orogenic crustal materials(especially accretionary crustal materials),mixing with some mantle-derived material,and experienced fractionation of feldspar and other minerals during the magma evolution.The tectonic regime may have been a compression-extension transition from syn-collisional to post-collisional setting.